Somatic mutations in isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2) were recently demonstrated in acute myeloid leukemia (AML), but their prevalence and prognostic impact remain to be explored in large extensively characterized AML series, and also in various other hematologic malignancies. Here, we demonstrate in 893 newly diagnosed cases of AML mutations in the IDH1 (6%) and IDH2 (11%) genes. Moreover, we identified IDH mutations in 2 JAK2 V617F myeloproliferative neoplasias (n = 96), a single case of acute lymphoblastic leukemia (n = 96), and none in chronic myeloid leukemias (n = 81). In AML, IDH1 and IDH2 mutations are more common among AML with normal karyotype and NPM1^mutant genotypes. IDH1 mutation status is an unfavorable prognostic factor as regards survival in a composite genotypic subset lacking FLT3^ITD and NPM1^mutant. Thus, IDH1 and IDH2 mutations are common genetic aberrations in AML, and IDH1 mutations may carry prognostic value in distinct subtypes of AML.